The present invention relates to a method and to a device for power distribution in a motor vehicle.
In known control systems of motor vehicle components, the software is structured according to functions. It may occur that different functions access the same actuating elements. Interchangeability of software parts is possible only at considerable expense. Modular development is not supported.
In order to improve this situation, German Published Patent Application No. 41 11 023 (corresponding to U.S. Pat. No. 5,351,776), for example, describes a control system and a control device making it possible to control the entire vehicle and having a hierarchical instruction structure for the control tasks. The control structure described in that patent includes coordination elements which convert an instruction originating from a higher hierarchical level into instructions for elements on a lower hierarchical level. The contents of the instructions transmitted from the top down in the hierarchical structure represent physical values which determine the interfaces between the different hierarchical levels. The described interfaces are oriented so as to agree with the physical conditions of the vehicle movement, in particular of the power train and the brake. No further possibilities of a vehicle control taking into consideration the power distribution in the vehicle""s electrical distribution system is described.
The installed electrical power may in some cases exceed 15 kW in the future. In the worst case, 7 kW continued electrical power is possible (this represents the extreme possible combination of loads with maximum capacity of the individual loads in normal operation). Additional actuation of short-term loads may cause this value to exceed 10 kW. When electrical motors and/or incandescent lamps are switched on at the same time, an additional, non-negligible output peak occurs which is caused by starting currents.
These numerical values clearly show the requirements imposed upon a vehicle""s electrical distribution system of the future. The battery or batteries and generator are designed so that the vehicle can be used at all times. This means that the electrical output is balanced on the average, with the boundary requirement that the battery charge state may not drop below a critical value so that the engine can be started at any time. The specified voltage limits may not be exceeded nor may the voltage fall below these limits so that load failures (e.g., control device failure due to insufficient voltage) may be avoided. Drive concepts of the future, such as start-stop systems or momentum-utilizing systems increase the demands made upon the vehicle electrical distribution system further, since a generator coupled to the engine produces no energy when the engine stops.
The production of electrical power also affects a vehicle""s fuel requirements. The production of 100 W of electrical energy raises the fuel requirements by approximately 0.17 liters/100 km. A 50-kg increase in the weight of the vehicle results in the same additional consumption. A reduction in the vehicle""s fuel requirement and at the same time significant increase in the electrical power is only possible if the efficiency of the power production, distribution and utilization is improved on the one hand while the interaction between the power train and the vehicle electrical distribution system is optimized on the other hand (overall efficiency).
An improvement in the overall efficiency can be achieved with the help of a vehicle electrical distribution system management which coordinates the control of the vehicle""s electrical system distribution components (e.g., generator, battery(ies), load, voltage regulator, DC/DC converter). Similarly, vehicle electrical distribution system management can reduce the worst-case demands on battery and generator (e.g., starting ability at xe2x88x9225xc2x0 C.). These rarely occurring cases can be mastered through measures taken by the vehicle""s electrical distribution management system (e.g., by increasing the rotational speed level of the drive or by reducing the load power consumption).
It is a object of the present invention to provide the structure of a vehicle electrical distribution system management using which the described requirements can be met and which is incorporated into a hierarchical control structure.
In German Patent Application No. 1 97 45 849.1 of Oct. 16, 1997 (not a prior publication), a vehicle""s electrical distribution system management is shown. The power distribution is implemented using a control system which operates as the vehicle""s electrical distribution system manager. The data is transmitted to the control unit which, on the basis of this data, implements a strategy for the control of the components of the vehicle electrical distribution system and of the internal combustion engine. The power distribution between the vehicle""s electrical distribution system and the internal combustion engine takes place in accordance with requirements that can be specified while taking into account that the vehicle""s electrical distribution system target voltage (U_s) lies within specified limits. The actual design of the vehicle electrical distribution system manager and integration into a hierarchical control structure are not described.
The principle of a basic hierarchical structure of an overall vehicle system is known from the German Patent Application No. 1 97 09 317.5 of Mar. 7, 1997, (also not a prior publication). In that application a vehicle coordinator determines the components: drive (source of mechanical power), vehicle movement, body and interior space and vehicle electrical distribution system (source of electrical power). The communication among the individual components of this structure takes place only between the higher-level component and the components assigned to it within the framework of fixed and predefined communication relations. These are the instructions given in principle by a component on a higher hierarchical level to a component on a lower hierarchical level and which are carried out by the assigned component, the request made also by a component on a lower hierarchical level of a component on a higher hierarchical level and which should be filled by the addressed component, and the query to which an answer by the queried component to the querying component is expected. The control of the vehicle takes place within the framework of these specified communication relations between the components. Fixed and predefined physical magnitudes representing interfaces defined between the individual components are transmitted to the control of the vehicle. No design of the coordinator vehicle""s electrical distribution system is shown.
The vehicle""s electrical distribution system manager described above makes the control of the vehicle""s electrical distribution system possible, and thereby makes it possible to embed the control of the power distribution in a hierarchical overall vehicle structure. Greater control over the entire system and over the power distribution control system is achieved in this manner, and modular development of software becomes thus possible. This is because an object-oriented structure of the vehicle""s electrical distribution system manager is specified in accordance with the structure of the overall system.
It is especially advantageous that this structure of the vehicle""s electrical distribution system and of the vehicle""s electrical distribution system manager is especially simple. The interfaces between the individual components, and the interchanged signals are purely of logical nature, i.e., independent of hardware and implementation (e.g., rotational speed, power, torque, voltage, etc.). The possibility of re-using software and easy expendability, straightforward overview and ease of applicability are the resulting advantages.
It is also an advantage that the vehicle""s electrical distribution system coordinator described in greater detail further below, coordinates the interaction among generator, voltage regulator, electrical loads, batteries and, if applicable, DC/DC transformers. Coordination with the power train is provided in a higher-level component (vehicle coordinator) above the coordinator of the vehicle""s electrical distribution system. In another embodiment a vehicle""s electrical distribution system manager is provided which in addition assumes the role of the higher-level component and also takes the power train into account. A suitable strategy for the production, distribution, storage and utilization of the electrical power is determined. This increases vehicle availability, because the loading balance is assured, the vehicle""s electrical distribution system voltage is maintained dynamically and statically within the specified range, the interaction between the vehicle""s electrical distribution system and the drive is improved and the life of the battery is extended. At the same time, as a boundary condition, fuel consumption is kept to a minimum.
Due to the structures described below, having a higher-level block coordinating the subordinate subsystem, the subsystems are coordinated optimally. The structure makes a higher-level power management possible.